Platypus genomic analysis and comparison
(Warren et al 2008) The platypus is a creature with many unique, and many would argue flat out strange, attributes. It was first believed to be a taxidermist’s hoax because of the many phenotypic features it shares with other animals across many species. Warren et al, in their 2008 Nature paper, observed the genomic makeup of the Platypus in comparison to creatures with similar phenotypic attributes (ex. reptiles and the production of venom). The species of comparable interest were therian mammals (marsupials and eutherians), and birds and reptiles (sauropsids) due to shared phenotypic traits with the platypus. Tissue samples were taken from Platypus specimens in New South Wales in Australia. FISH was used to map out the sequence scaffolds to chromosomes due to no linkage maps having previously been recorded. The non-protein coding regions were analyzed first. Of interest, Warren et al found that the genome contained less non-protein coding than mammals. However, the Platypus shared 40 families of microRNA with eutherians and not sauropsids, and 8 families of miRNA with sauropsids and not eutherians. Also found were 183 novel miRNA’s in the Platypus which are postulated to be associated with the highly unique monotreme reproductive and developmental biology. In observing the physiological traits of the platypus in concert with its genome, Warren et al made some anticipated correlations and some not so anticipated. The platypus expresses ordant genes which were not expected. The platypus was expected to use chemoreceptive genes indicative of a terrestrial exploring/foraging animal. However, they express a wider range of odorant receptors which show both similarities to terrestrial animals but also animals using odor receptors for water soluble odorants which are suggested to be used for under water foraging. Another unique attribute of their expanding genome for odor receptors is hypothesized to be used in a pheremonal detection system. An interesting finding is that the fertilization and development of the platypus has characteristics of both sauropsid and therians. For example, the platypus lays eggs, which derive from genes very similar to that of sauropsids which are involved in the development of eggs within the organism. The platypus also expresses marsupial and mammalian like behavioral/genetic traits in that thee egg hatches at a beginning stage of development, requiring the young to further mature within a pouch on the mother. It is in this pouch where a mammillary pouch without a nipple exists which lactates milk. The milk secreted in this location is fully developed milk (not egg protective milk like secretions proposed to be exhibited in sauropsids) which will provide essential nutrients to the developing young. The genes orchestrating these processes of lactation and development resemble more closely to genes expressed in therians. The finding of most interest was of the genetic components of the Platypus’ venom. The male platypus has venom which is excreted from a hook like spur on its hind legs. This venom was found, according to Warren et al, to be comprised of defensin like peptides, c-type natriuretic peptides, and nerve growth factors. The interesting fact was that the evolutionary development of this venom, believed to be conserved from the branching of sauropsids and the species that led to the platypus, evolved independently within the platypus. This development of venom showed convergent evolution as the development of venom in sauropsids such as snakes and other reptiles. Although both share important genetic aspects, these genotypic developments occurred independently of one another.